The blink reflex in migraine

Monitoring Migraine Cycle Dynamics with an Easy-to-Use Electrophysiological Marker-A Pilot Study

Migraine attacks can cause significant discomfort and reduced functioning for days at a time, including the pre-ictal and post-ictal periods. During the inter-ictsal period, however, migraineurs seem to function normally. It is puzzling, therefore, that event-related potentials of migraine patients often differ in the asymptomatic and inter-ictal period. Part of the electrophysiological dynamics demonstrated in the migraine cycle are attention related. In this pilot study we evaluated an easy-to-use new marker, the Brain Engagement Index (BEI), for attention monitoring during the migraine cycle. We sampled 12 migraine patients for 20 days within one calendar month. Each session consisted of subjects’ reports of stress level and migraine-related symptoms, and a 5 min EEG recording, with a 2-electrode EEG device, during an auditory oddball task. The first minute of the EEG sample was analyzed. Repetitive samples were also obtained from 10 healthy controls. The brain engagement index increased significantly during the pre-ictal (p ≈ 0.001) and the ictal (p ≈ 0.020) periods compared with the inter-ictal period. No difference was observed between the pre-ictal and ictal periods. Control subjects demonstrated intermediate Brain Engagement Index values, that is, higher than inter-ictal, yet lower than pre-ictal. Our preliminary results demonstrate the potential advantage of the use of a simple EEG system for improved prediction of migraine attacks. Further study is required to evaluate the efficacy of the Brain Engagement Index in monitoring the migraine cycle and the possible effects of interventions.

Abnormal Habituation of ‘nociceptive’ Blink Reflex in Migraine-Evidence for Increased Excitability of Trigeminal Nociception

We studied the habituation of the ‘nociceptive’ blink reflex (nBR) in 15 healthy subjects and 17 migraine patients interictally as well as during unilateral migraine headache within six hours of onset and after treatment. In healthy volunteers the mean regression coefficient (MRC) was – 3.9 following right sided and – 4.9 left sided stimulation. This equals an amplitude loss of 19.5% (5 X −3.9) and 24.5% (5 X −4.9), respectively, across five consecutive sweeps. An augmentation of nBR responses was found in migraine patients interictally: MRC = 3.3 following stimulation of the headache side (HA) and MRC = 4.0 of the non-headache side (non-HA). The differences were statistically significant (ANOVA: d.f. = 1, F = 25.8, P < 0.001). During the migraine attack MRCs were negative both before (−5.0, HA and – 4.0, non-HA) and after treatment (−2.6, HA and −1.9 non-HA) and significantly differed from those outside the migraine attack (ANOVA: d.f. = 2, F = 12.4, P < 0.001). The demonstrated lack of habituation of the nBR responses indicates an abnormal trigeminal nociceptive processing in migraine patients outside the migraine attack.

Deficient prepulse inhibition of blink reflex in migraine and its relation to allodynia

OBJECTIVE

Prepulse inhibition (PPI) of the blink reflex (BR) is a reduction in BR excitability due to a conditioning stimulus, reflecting sensory gating by brainstem structures. We aimed to analyze PPI changes during a painful episode in chronic or episodic migraine and its relation to allodynia, since abnormal brainstem filtering has been hypothesized in migraine pathophysiology.

METHODS

We included 20 patients with migraine during headache episode, and age- and gender-matched 22 healthy subjects. We recorded BR after unconditioned and conditioned supraorbital stimuli. For conditioned stimuli, we applied preceding subthreshold stimulus to the median nerve at wrist. The presence of PPI was compared between the two groups, as well as the specific BR parameters (latency, amplitude or area of R1 and R2 components) in unconditioned (test) and conditioned (PPI) paradigms.

RESULTS

In the patient group, seven (35%) patients did not have R2-PPI whereas all healthy subjects had R2-PPI (P=0.003). Healthy subjects displayed significantly increased R1 amplitude and reduced R2 amplitude and area after conditioned stimuli. In migraine patients, we observed significant reduction only in R2 amplitude. Logistic regression demonstrated that allodynia was independently related with the presence of PPI (beta: -0.535, P=0.021).

CONCLUSIONS

Our study provides evidence for sensory gating impairment at brainstem level in migraine headache, related to the presence of allodynia.

Exteroceptive Suppression of Masseter Muscle Activity in Juvenile Migraineurs

The second exteroceptive suppression period (ES2) of masseter or temporalis muscle activity may be reduced in adults with chronic tension-type headache. In adults with migraine, ES2 was found normal or tended to be protracted. To date, no studies on exteroceptive suppression in children and adolescents with headaches have been published. We investigated the exteroceptive suppression of masseter muscle activity in 14 migraineurs and 19 controls between 6 and 18 years of age. It was elicited by electrical stimulation at the labial commissure. No differences were found regarding the first suppression period, but ES2 was significantly longer in the migraine group than in controls. The results of the migraine group suggest overactivity of the interneurons of the reflex loop due to impaired inhibitory control from superior antinociceptive systems already at the beginning of this headache disorder.

Blink reflex in migraine headache

OBJECTIVE:

Activation of trigeminovascular system is thought to play an important role in migraine pathogenesis. Blink reflex (BR) test is an easy method to study the trigeminal system. Latencies recorded in BR test were evaluated to examine neurophysiological changes that occur in migraine patients.

METHODS:

A total of 40 patients diagnosed with migraine (9 with aura and 31 without aura) according to the International Headache Society (IHS) International Classification of Headache Disorders, 2nd edition, and 30 healthy control subjects were assessed using BR test. Supraorbital nerve was stimulated on each side, and unilateral early component (R1), and bilateral late component (R2) latencies were evaluated.

RESULTS:

Significantly longer latency values were recorded on both right and left sides (RR1 and LR1) as well as both ipsilateral and contralateral R2 on the left side (LR2i and LR2c) in the migraine group compared to the control group. Longer RR1 and LR1 latencies were found in patients with migraine who had an attack at the time of study (p<0.01). There was no statistically significant correlation between the location of pain and latencies in the interictal period (p>0.05). But significantly longer R1 and R2i latencies were found at the symptomatic side of patients examined during the headache attack (p=0.037 and p=0.028 respectively). There was no statistically significant correlation between the recorded latencies and gender, attack duration, attack frequency and migraine type (p>0.05).

CONCLUSION:

Results of BR test in the present study are thought to point to a dysfunction in brainstem and trigeminovascular connections of patients with migraine headache and support the trigeminovascular theory of migraine.

Trigeminal somatosensorial evoked potentials suggest increased excitability during interictal period in patients with long disease duration in migraine

INTRODUCTION

Migraine pathogenesis is suggested to involve many structures in cerebral cortex, brainstem and trigeminovascular system. Electrophysiological studies revealed loss of habituation, decreased cortical preactivation, segmental hypersensitivity and reduction in control of inhibitory descending pathways. Given these information, we aimed to evaluate the excitability changes of the trigeminal pathway in the cortex and brainstem in migraine using trigeminal nerve somatosensory evoked potentials (TSEP).

PATIENTS AND METHOD

Fifty-one women with migraine without aura and 32 age-matched healthy women were included. TSEPs were recorded in migraine patients during interictal period and in healthy subjects. Sensory thresholds, stimulation intensities, latencies of N1, P1, N2 and P2 waves as well as N1/P1 and N2/P1 amplitudes were measured.

RESULTS

Comparisons of ipsilateral latencies with N1-P1 and N2-P1 amplitudes between migraine and control groups showed no difference. Sensory thresholds were also similar. Stimulation thresholds decreased as the attack frequency increased and ipsilateral N1/P1 amplitude increased with prolonged disease duration (p=0.043).

CONCLUSION

Our study did not show significant difference between migraine patients and healthy subjects during interictal period. However, migraine with long duration affects the excitability of the cortical and brainstem trigeminal pathways even during interictal periods.

The role of the trigeminal sensory nuclear complex in the pathophysiology of craniocervical dystonia

Isolated focal dystonia is a neurological disorder that manifests as repetitive involuntary spasms and/or aberrant postures of the affected body part. Craniocervical dystonia involves muscles of the eye, jaw, larynx, or neck. The pathophysiology is unclear, and effective therapies are limited. One mechanism for increased muscle activity in craniocervical dystonia is loss of inhibition involving the trigeminal sensory nuclear complex (TSNC). The TSNC is tightly integrated into functionally connected regions subserving sensorimotor control of the neck and face. It mediates both excitatory and inhibitory reflexes of the jaw, face, and neck. These reflexes are often aberrant in craniocervical dystonia, leading to our hypothesis that the TSNC may play a central role in these particular focal dystonias. In this review, we present a hypothetical extended brain network model that includes the TSNC in describing the pathophysiology of craniocervical dystonia. Our model suggests the TSNC may become hyperexcitable due to loss of tonic inhibition by functionally connected motor nuclei such as the motor cortex, basal ganglia, and cerebellum. Disordered sensory input from trigeminal nerve afferents, such as aberrant feedback from dystonic muscles, may continue to potentiate brainstem circuits subserving craniocervical muscle control. We suggest that potentiation of the TSNC may also contribute to disordered sensorimotor control of face and neck muscles via ascending and cortical descending projections. Better understanding of the role of the TSNC within the extended neural network contributing to the pathophysiology of craniocervical dystonia may facilitate the development of new therapies such as noninvasive brain stimulation.

Where does a migraine attack originate? In the brainstem

Migraine is a common, paroxysmal, highly disabling primary headache disorder. The origin of migraine attacks is enigmatic. Numerous clinical and experimental results suggest that the activation of distinct brainstem nuclei is crucial in its pathogenesis, but the primary cause of this activation is not fully understood. We conclude that the initialization of a migraine attack can be explained as an altered function of the neuronal elements of the brainstem nuclei. In light of our findings and the literature data, we can assume that migraine is a subcortical disorder of a specific brainstem area.

Change of Excitability in Brainstem and Cortical Visual Processing in Migraine Exhibiting Allodynia

BACKGROUND

Clinical and neurophysiological manifestations of information processing associated with central sensitization are little known. Allodynic migraine (AM) can be caused by the sensitization of trigeminal neuron, but no study has reported on AM between attacks using blink reflex (BR) and pattern-reversal visual evoked potentials (PVEPs).

OBJECTIVE

We explored the characteristics of AM between attacks associated with central sensitization using BR and PVEP.

METHODS

We recruited 13 patients with interictal AM and 15 patients with nonallodynic migraine (NA), and 30 healthy subjects (HS). BRs were obtained using paired pulses delivered at the interstimulus interval (ISI) of 150, 300, and 500 ms. The ratio of the area in the R2 of the second to R2 of the first shock was measured for each ISI. PVEP were recorded with 2 spatial frequencies (0.5 and 4.0 cpd) and 2 low and high contrasts (29% and 98%, respectively). Amplitudes of P100 were measured.

RESULTS

For BR, there were no significant differences in the ratio of the area of the R2 between the sides of stimulation, and the sides of headache. AM patients had less suppression of the R2 at the ISI of 150 and 300 ms when compared with the NA patients and HS. For PVEP, at 0.5, there were significant differences of amplitude between AM patients and HS, and between NA patients and HS in low and high contrast. At 4.0 cpd, there were significant differences of amplitude between AM patients and HS in low contrast, and between AM patients and HS, and NA patients and HS in high contrast. In AM patients, there was a significant difference of amplitude ratio between 0.5 and 4.0 cpd. Conclusions.-Our BR and PVEP study showed that migraine patients exhibiting allodynia may show central sensitization of brainstem trigeminal neuron and have contrast modulating dysfunction during the cortical visual processing of striate and extrastriate on visual cortex in-between attacks.

Enhanced trigemino-cervical-spinal reflex recovery cycle in pain-free migraineurs

OBJECTIVE

To evaluate trigemino-cervical-spinal reflexes (TCSRs) in a group of migraine patients during the pain-free period.

BACKGROUND

TCRSs are part of a complex nocifensive response involving the cervical and the upper limb muscles, and are modulated by supraspinal inhibitory pathways; it may, thus, be possible to use TCRSs to explore the trigeminal system in migraineurs.

METHODS

A total of 43 migraine patients without aura (MWoA, 32 patients) or with typical aura (MWA, 11 patients) and 30 age- and sex-matched healthy subjects took part in the study. TCRSs were obtained by stimulating the supraorbital nerve and recorded from the semispinalis capitis muscle and the biceps brachii. The latency (L, msec), area (A, mVms) and recovery cycle of the reflexes were recorded. The effects of heterotopic painful stimulation on the neurophysiological parameters were studied by a validated cold pressor test (CPT).

RESULTS

No significant changes were found between either migraine patients and controls or MWoA and MWA patients in the mean values in the L and A of TCRSs (t-test, P > .05). The recovery curve of the trigemino-cervical reflexes (TCRs) was significantly faster in migraine patients than in controls, while no differences were found in the trigemino-spinal reflexes (TSRs) (t-test, P < .01). Activation of the diffuse inhibitory controls through the CPT induced a significant reduction in the TCRs and TSRs area in both migraine patients and controls (paired t-test, P < .01), though the extent of this reduction did not differ significantly between migraineurs and controls (t-test, P > .05).

COMMENTS

Our data suggest that the pain-free period in migraine patients is characterized by a hyperexcitability of the trigeminal pathways and of their anatomical and functional connections with the upper cervical cord neurons, and that this abnormal hyperexcitability does not appear to be due to a lack of a supraspinal inhibitory modulation.

Electrophysiological studies in migraine: a comprehensive review of their interest and limitations

Electrophysiological methods may help to unravel some of the pathophysiological mechanisms of migraine. Lack of habituation is the principal and most reproducible interictal abnormality in sensory processing in migraineurs. It is found in evoked potential (EP) studies for every stimulation modality including nociceptive stimuli, and it is likely to be responsible for the increased intensity dependence of EP. We have hypothesized that deficient EP habituation in migraine could be due to a reduced preactivation level of sensory cortices because of hypofunctioning subcortico-cortical aminergic pathways. This is not in keeping with simple hyperexcitability of the cortex, which has been suggested by some, but not all, studies of transcranial magnetic stimulation (TMS). A recent study of the effects of repetitive TMS on visual EP strongly supports the hypothesis that migraine is characterized by interictal cortical hypoexcitability. With regard to pain mechanisms in migraine, electrophysiological studies of trigeminal pathways using nociceptive blink and corneal reflexes have confirmed that sensitization of central trigeminal nociceptors occurs during migraine attacks.

Trigeminofacial reflexes in primary headaches

Nociceptive processing in trigeminal system is likely to undergo to significant changes in chronic pain disorders such as in primary headache. The electrophysiological testing of brainstem reflexes seems to offer a valuable adjunct to the clinical evaluation, providing direct evidence for central dysmodulation of sensory and pain neurotransmission, i.e. dishabituation pattern and reduced pain threshold. We review the contribution of trigeminofacial reflex studies in the light of those recent data supporting the view of a dysfunctional sensory processing in primary headache.

Nociceptive-specific blink reflex and glyceryl trinitrate infusion in healthy volunteers

Glyceryl trinitrate (GTN) is known to induce early headache in healthy humans after intravenous infusion. Moreover, in animal models subcutaneous administration produces an increase in Fos expression in brainstem areas that are involved in trigeminal pain processing. In a double-blind crossover study, we tested the blink reflex before, during and immediately after GTN and placebo intravenous infusion in eight healthy volunteers using a new stimulation electrode that preferentially activates A-delta nociceptive afferent fibres. The initial hypothesis that GTN could induce an increase in the magnitude of the nociceptive blink reflex R2 component by stimulating activity of trigeminal nucleus caudalis wide dynamic range interneurones was not confirmed. Although mild headache was induced in six subjects, there was no significant change between the R2 area under the curve before and after drug vs. placebo.

Exteroceptive suppression patterns of masseter and temporalis muscles in central and peripheral headache disorders

The objective of this study was to compare the exteroceptive suppression patterns of masseter and temporalis muscles in patients with primary and secondary headache disorders originating from peripheral joint dysfunction. We accomplished the temporalis and masseter exteroceptive suppression in 28 patients with migraine, 25 patients with chronic tension-type headache (CTH), 22 patients with temporomandibular joint (TMJ) dysfunction and 18 healthy controls. The onset latencies and duration of the first suppression period (S1) was not significantly different between the patients and controls. The duration of the second suppression period (S2) was shorter in patients with CTH, migraine (analysed during attack) and TMJ dysfunction than those obtained from controls. A distinctive finding was significantly prolonged onset latency in patients with TMJ over those obtained from patients with CTH and migraine. We concluded that the onset latency of the S2 period is a useful parameter in the differential diagnosis of primary and peripheral headache disorders.

Modulation of trigeminal reflex excitability in migraine: effects of attention and habituation on the blink reflex

The modulation of trigeminal reflex excitability in migraine patients was evaluated during the asymptomatic phase by studying the effects of attention, habituation and preconditioning stimulus on the R2 and R3 components of the blink reflex (BR). Fifty patients suffering from migraine without aura, 20 affected by migraine with aura and 35 sex- and age-matched controls were selected. In subgroups of migraine with-aura and without-aura patients, and normal controls, the blink reflex was elicited during different cognitive situations: (a) spontaneous mental activity; (b) stimulus anticipation; (c) recognition of target numbers. In the remaining subjects, R2 and R3 habituation was evaluated by repetitive stimulation at 1, 5, 10, 15, 20, 25 and 30 s intervals. The R2 and R3 recovery curves were also computed. A reduced R3 threshold with a normal pain threshold was found in migraine with-aura and without-aura patients; the R3 component was not significantly correlated with the pain thresholds in patients and controls. The R2 and R3 components were less influenced by the warning of the stimulus in migraine without-aura and migraine with-aura patients, in comparison with the control group. A slight increase of both R2 and R3 recovery after preconditioning stimulus was also observed in migraine patients, probably caused by a phenomenon of trigeminal hyperexcitability persisting after the last attack. The abnormal BR modulation by alerting expresses in migraine a dysfunction of adaptation capacity to environmental conditions, probably predisposing to migraine.

Acute migraine headache: possible sensitization of neurons in the spinal trigeminal nucleus?

OBJECTIVE

To investigate trigeminal sensory processing in patients with migraine using a novel "nociception-specific" blink reflex.

METHODS

Seventeen patients with unilateral migraine headache were studied within 6 hours of onset. Blink reflexes were elicited with a standard stimulating electrode (standard blink reflex) and concentric stimulating electrode (nociception-specific blink reflex) during the acute migraine attack, after treatment with IV lysine acetylsalicylate (1,000 mg) or oral zolmitriptan (5 mg) and interictally.

RESULTS

After standard stimulation, no differences were detected for the R1 and R2 onset latencies and areas under the curve (AUC) between the different time points and the headache and nonheadache side. Nociception-specific stimulation revealed a shortening of R2 onset latencies (44.3 +/- 5.4 ms for headache side vs 48.9 +/- 5.8 ms for nonheadache side) during the acute migraine attack compared with the headache-free interval (49.8 +/- 5.3 vs 49.8 +/- 4.5 ms). The AUC of the R2 increased on the headache side by 680% and on the nonheadache side by 230% compared with the headache-free interval. Drug treatment parallel to pain relief increased the onset latencies (zolmitriptan: 48.0 +/- 8.2 ms for headache side vs 52.3 +/- 7.6 ms for nonheadache side; lysine acetylsalicylate: 48.0 +/- 5.0 ms for headache side vs 51.2 +/- 5.6 ms for nonheadache side) and reduced the AUC of R2 (zolmitriptan by 45% and lysine acetylsalicylate by 48%).

CONCLUSION

The data suggest temporary sensitization of central trigeminal neurons during acute migraine attacks.

Electrophysiological evidence for trigeminal neuron sensitization in patients with migraine

The electrically elicited corneal reflex is a useful tool for exploring the trigeminal system in humans and it may provide additional evidence pointing to a dysfunction of this system in migrainous patients. Tactile perception, corneal reflex and pain thresholds were studied in 48 migraine without aura patients during pain-free periods and compared with those observed in 24 controls. Twenty-eight of the patients had strictly unilateral headache, while the other 20 had bilateral or side-shifting pain during attacks. Both migraine subgroups (bilateral and unilateral) showed significantly lower thresholds compared with controls. The lowest values were observed on the symptomatic side of unilateral migraine patients. These findings suggest that sensorimotor mechanisms and/or pain control systems at the trigeminal level are impaired in migraine. The bilateral location of these abnormalities seems to point to a centrally located dysfunction.

Recovery cycle of the blink reflex and exteroceptive suppression of temporalis muscle activity in migraine and tension-type headache

Brain stem interneuronal excitability can be assessed by recording the recovery cycle of the blink reflex and exteroceptive suppression of temporalis muscle activity. Abnormal endogenous pain control mechanisms due to disturbed brain stem interneuronal activity have been implicated in the pathogenesis of tension-type headaches. The blink reflex, exteroceptive suppression of temporalis muscle activity, and the recovery curve of both the R2 component of the blink reflex and the ES2 component of the exteroceptive suppression of the temporalis muscle activity were studied in 20 patients with migraine without aura, 32 patients with tension-type headache, and 20 normal controls. In our study, the blink reflex was elicited by stimulation of the supraorbital nerve; the exteroceptive suppression of the temporalis muscle activity was elicited by applying electrical shocks to the labial commissure, both on the lower and upper sides. The recovery cycle was established by delivering paired shocks at different interstimulus intervals. Comparisons were made between normal control subjects, patients with migraine without aura, and patients with tension-type headache. The latency of R1, R2, and R2', the amplitude and size of the R2 and R2' components of the blink reflex, the latency and duration of the ES1 and ES2 components, and the recovery curve of the ES2 component of the temporalis muscle activity did not differ between groups. However, the recovery curve of the R2 component of the blink reflex diminished in patients with tension-type headache compared with the other groups. Our findings indicate reduced excitability of the brain stem interneurons in patients with tension-type headache.

The clinical use of brainstem reflexes and hand-muscle reflexes

Brainstem reflexes and hand-muscle reflexes can be elicited and recorded with routine EMG equipment. Not all these reflexes are useful in clinical neurology. But those that are - the subject of this review - exhibit distinct patterns of abnormality that have clinical diagnostic and localizing value in various diseases, including cranial neuropathies, focal lesions within the cervical cord, brainstem, and brain, movement disorders, and pain.

Clinical neurophysiology of headache

Methods of clinical neurophysiology are of little use for the diagnosis of headache disorders. They are, however, invaluable tools for a better understanding of the pathophysiology of functional headaches. They are traumatic, able to explore simple or more complex neural activities, and to some extent capable of reflecting activity in certain neurotransmitter systems as well as the action of pharmacologic agents on the CNS. This article reviews the interest and limits of electroencephalography, evoked potentials, electromyography, and nocifensive reflexes in primary headaches. Because neurophysiologic methods are no more than indirect means of looking into the "black box," their results need to be interpreted with caution and, whenever possible, should be compared in the same study with clinical behavioral and biochemical data.

Electrophysiological study of blink reflex in humans: differences in mental and supraorbital nerves

In order to find an explanation for the discrepancy between previous reports on the consistency of the blink reflex response with stimulation of the mental nerve, the habituation of the blink reflex was studied with stimulation of the supraorbital and mental nerves in 14 healthy adults. A series of eight electrical stimuli was delivered to the distributions of the nerves on each side at frequency rates of 1.0, 0.5, 0.2 and 0.1 Hz. The latencies and peak-to-peak amplitudes of the ipsilateral late blink reflex components (R2i) were measured. The habituation phenomenon was analysed by means of multivariate analysis of the amplitudes, the nerve and frequency effects were determined by means of a repeated measures analysis of variance model. The blink reflex showed more pronounced amplitude attenuation of the consecutive responses with stimulation of the mental than the supraorbital nerve at rates of 0.5 and 0.2 Hz, and marginally so also at 0.1 Hz. For the supraorbital nerve, habituation could be demonstrated with stimulation frequencies of 1.0 and 0.5 Hz, while for the mental nerve a statistically significant habituation phenomenon was found even with the lowest repetition rate of 0.1 Hz. The greater tendency of the mental nerve blink reflex to habituate is obviously one reason why it has previously sometimes been considered too inconsistent to be useful in clinical practice. For the recording of the supraorbital nerve blink reflex, a 10 s interval between stimuli is adequate, whereas longer interstimulus intervals may have to be adopted to obtain consistent blink reflex responses with stimulation of the mental nerve.